DC regulated power supply

ABSTRACT

A DC regulated power supply includes: a power transistor provided for each output of a plurality of systems; a control IC, which compares a feedback value of an output voltage and a reference voltage from a reference voltage source, and controls a base current of the power transistor according to a difference of the feedback value and the reference voltage, so as to regulate the output voltage; and an overheat protection circuit, which lowers the reference voltage of the reference voltage source upon detecting an overheated state in the power transistor. The DC regulated power supply is able to simultaneously suppress transistor base currents of different systems and eliminate regulation malfunctions in the overheat protection operation, thereby suppressing fluctuations of output voltage.

FIELD OF THE INVENTION

The present invention relates to a DC regulated power supply of adropper-type, known as a series regulator, and particularly to astructure for the protection against overheating in such a DC regulatedpower supply with outputs of plural systems.

BACKGROUND OF THE INVENTION

FIG. 6 is a block diagram illustrating a basic electrical structure of adropper-type DC regulated power supply 1. The DC regulated power supply1 is a three-terminal regulator with a single output, in which a powertransistor q is interposed in series on a power line 1 that connects apower supply with a load (neither is shown). The base current of thepower transistor q is controlled by a control IC ctl. In this way, anoutput voltage vo is adjusted to an output voltage level that has beenset beforehand according to the load requirement, thereby generating astable DC voltage.

In the control IC ctl, a differential amplifier a compares a referencevoltage vref from a reference voltage source 2 with a feedback voltagevadj, the reference voltage source 2 being provided either internally orexternally to the control IC ctl (internally in the example shown inFIG. 6), and the feedback voltage vadj being produced by dividing theoutput voltage vo through resistors r1, r2. By thus comparing the twovoltages, the differential amplifier a controls the base current of thepower transistor q via a control transistor tr, so as to match the twovoltages. On the output side of the power transistor q is provided anoutput capacitor (not shown) for smoothing the output.

The DC regulated power supply 1 with the described structure generallyincludes a protection circuit, such as an overcurrent protection circuitb and an overheat protection circuit 3, by which the base current of thepower transistor q is reduced when an overcurrent flows or when there isa temperature increase in the series regulator, so as to protect the DCregulated power supply 1.

However, the DC regulated power supply 1 has a drawback in that theoperation of the protection circuit influences other output systems whenthe output of more than one system is packed and sealed in a singlepackage. This is due to the fact that the DC regulated power supply 1 isa single-output regulator, whereby the circuits of each functional blockare designed for single output.

FIG. 7 is a block diagram showing an electrical structure of a DCregulated power supply 11 with outputs of multiple systems (two systemsin FIG. 7). The DC regulated power supply 11 is realized by connecting aplurality of DC regulated power supplies 1 of the single-outputstructure in parallel, using a common input. In FIG. 7, the samereference numerals are used for the constituting elements that werealready described with reference to FIG. 6, and like elements areindicated by adding numbers.

In the DC regulated power supply 11 having the foregoing structure, upondetecting an overcurrent state, overcurrent protection circuits b1, b2bypass the base currents that are respectively supplied fromdifferential amplifiers a1, a2, so as to control transistors tr1, tr2.This reduces the base currents of the corresponding power transistorsq1, q2, thereby carrying out the protection operation.

Similarly, when an overheated state is detected in the overheatprotection circuit 3, the base currents supplied to the controltransistors tr1, tr2 are bypassed to reduce the base currents of thepower transistors q1, q2, thereby carrying out the protection operation.

Thus, in the DC regulated power supply 11, reducing the base currents bythe overheat protection circuit 3 in an overheated state effects theoverheat protection operation only in one of the systems, owning todifferences in circuit constant or load condition, i.e., differences inthreshold of the transistors due to different values of the basecurrents, which shifts the temperature (timing) of reducing the basecurrents from each other.

Here, fluctuations of the driving current causes the driving current ofthe other system to fluctuate, causing the output voltage to fluctuate.Particularly, when the output voltage increases and exceeds anacceptable voltage range of the load, the load may be damaged.

The overheat protection circuits of the DC regulated power supply 11operate when the temperature exceeds an overheat protection temperature.Below the overheat protection temperature, the overheat protectioncircuits do not operate and the DC regulated power supply 11 carries outnormal regulation operation.

As described above, the overheat protection circuits of the DC regulatedpower supply 11 operate at different timings. Accordingly, when theoverheat protection circuits operate in response to generated heat ofthe regulator and when the overheat protection operation becomeseffective only in one of the systems under a maintained devicetemperature in the vicinity of the overheat protection temperature, theoutput of the protected system may place the other system under theinfluence of driving current fluctuations for an extended period oftime.

Such a phenomenon is especially prominent when one of the systems has anexcessively small output current and the overheat protection circuitoperates in response to generated heat caused by the output current ofthe other system. FIG. 8 describes how this gives rise to malfunctions,with reference to respective waveforms of chip temperature, outputvoltage, output current, and input current.

When the output current of one system is excessively small, the overheatprotection circuit of the other system that has generated heat operatesand reduces only the current of the output that generated heat. Here,when the output current becomes temporarily dull, the input current alsobecomes dull if the capacity of the power supply is not sufficient. Theoutput with excessively small output current becomes more susceptible tothe influence of the dull input current as the current becomes smaller.This may result in regulation control failure or regulator malfunction.In the worst case, the output voltage vo increases above the pre-setvoltage to cause damage to the load devices. Thus, the multi-outputregulator needs to be designed such that the operation of one systemdoes not affect the operations of the other systems.

This is particularly true in one-chip configuration. Depending on thelayout of a semiconductor circuit block, operations of the control IC orprotection circuit of one system may cause potential fluctuations due toheat transfer or current flow even when the other systems are notoperating. This becomes more likely as the circuit distance within thechip becomes shorter. Further, even when the circuit design is the same,a common circuit component may cause differences in circuit constant dueto a distance therefrom or due to asymmetricity of the circuit. It istherefore required that the circuits be designed to minimize theinfluence of one system over another.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a DC regulated powersupply that can suppress fluctuations of output voltage caused byregulation malfunctions in overheat protection operation.

In order to achieve the foregoing object, a DC regulated power supply ofthe present invention includes: a power transistor provided for eachoutput of a plurality of systems; a control circuit, which compares afeedback value of an output voltage and a reference voltage from areference voltage source, and controls a base current of the powertransistor according to a difference of the feedback value and thereference voltage, so as to regulate the output voltage; and an overheatprotection circuit, which lowers the reference voltage of the referencevoltage source upon detecting an overheated state in the powertransistor.

With this configuration, a DC regulated power supply of a dropper typecan be realized that includes: outputs of multiple systems; a powertransistor serially interposed for each output on a power line thatconnects a DC power supply with a DC load; and a control circuit, whichcompares a feedback value that is obtained from the output voltage witha reference voltage from a reference voltage source, and controls a basecurrent of the power transistor according to the difference and therebycontrols the ON resistance of the power transistor, so as to regulatethe output voltage. The feedback value may be obtained by dividing theoutput voltage through the resistors.

With this configuration, in carrying out the overheat protectionoperation, the overheat protection circuit of the present inventionsuppresses the output current by lowering the reference voltage. Thiscontrasts to conventional overheat protection circuits, which suppressthe base current of the power transistor to suppress the output current.

The present invention is therefore able to simultaneously suppress thebase currents of different systems and eliminate regulation malfunctionsin the overheat protection operation, thereby suppressing fluctuationsof output voltage. The present invention is particularly suitable inapplications where a control circuit with multiple systems areintegrated into one chip and packaged into a single package with thepower transistor.

In order to achieve the foregoing object, another DC regulated powersupply of the present invention includes: a power transistor providedfor each output of a plurality of systems; a control circuit, whichcompares a feedback value of an output voltage and a reference voltagefrom a reference voltage source, and controls a base current of thepower transistor according to a difference of the feedback value and thereference voltage, so as to regulate the output voltage; and an overheatprotection circuit, which cuts off a supply line of an input voltage tothe power transistor upon detecting an overheated state in the powertransistor.

With this configuration, a DC regulated power supply of a dropper typecan be realized that includes: outputs of multiple systems; a powertransistor serially interposed for each output on a power line thatconnects a DC power supply with a DC load; and a control circuit, whichcompares a feedback value that is obtained from the output voltage witha predetermined reference voltage, and controls a base current of thepower transistor according to the difference and thereby controls the ONresistance of the power transistor, so as to regulate the outputvoltage. The feedback value may be obtained by dividing the outputvoltage through the resistors.

With this configuration, in carrying out the overheat protectionoperation, the overheat protection circuit of the present inventionsuppresses the output current by cutting off the supply line of an inputvoltage. This contrasts to conventional overheat protection circuits,which suppress the base current of the power transistor to suppress theoutput current.

The present invention is therefore able to suppress the regulationoperation of the entire DC regulated power supply to prevent theregulation operation of one system from influencing the regulationoperations of the other systems. This eliminates regulation malfunctionsin the overheat protection operation, and thereby suppressesfluctuations of output voltage.

For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an electrical structure of a DCregulated power supply of a First Embodiment of the present invention.

FIG. 2 is a block diagram showing an electrical structure of a DCregulated power supply of a Second Embodiment of the present invention.

FIG. 3 is a block diagram showing an electrical structure of a DCregulated power supply of a Third Embodiment of the present invention.

FIG. 4 is a block diagram showing an electrical structure of a DCregulated power supply of a Fourth Embodiment of the present invention.

FIG. 5 is a block diagram showing an electrical structure of a DCregulated power supply of a Fifth Embodiment of the present invention.

FIG. 6 is a block diagram showing a basic electrical structure of a DCregulated power supply of a dropper type.

FIG. 7 is a block diagram showing an electrical structure of a DCregulated power supply with outputs of multiple systems.

FIG. 8 is a waveform chart explaining operations of an overheatprotection circuit.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

Referring to FIG. 1, the following describes one embodiment of thepresent invention.

FIG. 1 is a block diagram illustrating an electrical structure of a DCregulated power supply 21 of the First Embodiment of the presentinvention. The DC regulated power supply 21 is a regulated power supplyof a dropper type, in which output voltages Vo1, Vo2 of two systems areproduced from a common input voltage Vin.

The output voltages Vo1, Vo2 of two systems may have the same level ordifferent levels. Likewise, the current capacitance may be the same ordifferent. Further, the number of systems is not just limited to two,and outputs of three or more systems may be used.

Power transistors Q1, Q2 are serially and respectively connected topower lines L1, L2 that connect a common power supply (not shown) totheir respective loads. Control ICs CTL1, CTL2 are provided to controlthe base currents of the power transistors Q1, Q2, respectively. Bycontrolling the base currents of the power transistors Q1, Q2, thecontrol ICs CTL1, CTL2 adjust the output voltages Vo1, Vo2 to outputvoltage levels that have been set beforehand according to the loadrequirement, and thereby generate stable DC voltages for the respectivesystems.

In the control IC CTL1, as in the control IC ctl, a differentialamplifier A1 compares a reference voltage Vref from a reference voltagesource 22 with a feedback voltage Vadj1 that has been produced bydividing the output voltage Vo1 through resistors R11 and R12. By thuscomparing the two voltages, the differential amplifier A1 controls thebase current of the power transistor Q1 via a control transistor TR1, soas to match the two voltages.

Similarly, in the control IC CTL2, a differential amplifier A2 comparesa reference voltage Vref from the reference voltage source 22 with afeedback voltage Vadj2 that has been produced by dividing the outputvoltage Vo2 through resistors R21 and R22. By thus comparing the twovoltages, the differential amplifier A2 controls the base current of thepower transistor Q2 via a control transistor TR2, so as to match the twovoltages.

The input voltage Vin supplies power to the circuits in the control ICsCTL1, CTL2. On the output sides of the power transistors Q1, Q2 arerespectively provided output capacitors (not shown) for smoothingoutputs.

The control ICs CTL1, CTL2 further include overcurrent protectioncircuits B1, B2, respectively. The overcurrent protection circuits B1,B2 detect the base currents of the power transistors Q1, Q2 from theemitter currents of the control transistors TR1, TR2. That is, theoutput currents of the power transistors Q1, Q2 are detected. When thedetected output currents are at or greater than a predetermined level,the overcurrent protection circuits B1, B2 bypass the base currents thatare supplied from the differential amplifiers A1, A2 to the controltransistors TR1, TR2, so as to effect the overcurrent protectionoperation for suppressing output current.

The control ICs CTL1, CTL2 are externally provided with an overheatprotection circuit 23. The overheat protection circuit 23 includestemperature detecting elements S1, S2, respectively corresponding to thepower transistors Q1, Q2. The temperature detecting elements S1, S2 arerespectively provided in the vicinity of the power transistors Q1, Q2.The overheat protection circuit 23, upon detecting an overheated statein at least one of the power transistors Q1, Q2, lowers the referencevoltage Vref from the reference voltage source 22.

In this way, it is possible to simultaneously suppress the base currentsof the power transistors Q1, Q2 of the two systems, so as to preventregulation malfunctions caused by overheat protection operation, therebysuppressing fluctuations of the output voltages Vo1, Vo2.

The power transistors Q1, Q2, the control ICs CTL1, CTL2, the resistorsR11, R12, and R21, R22, the reference voltage source 22, and theoverheat protection circuit 23 are packed and sealed in a singlepackage. This is highly advantageous in miniaturizing the device andsaving space therefor. Further, because the system responsible for thefeedback of the output voltage during stable operation and for thecurrent driving excludes the reference voltage source 22 and theoverheat protection circuit 23, these components can be shared betweenthe two output systems. This is even more advantageous for theminiaturization of the device.

Second Embodiment

The following describes another embodiment of the present invention.

FIG. 2 is a block diagram illustrating an electrical structure of a DCregulated power supply 31 of the Second Embodiment of the presentinvention. The DC regulated power supply 31 is similar to the DCregulated power supply 21, and accordingly corresponding elements aregiven the same reference numerals and explanations thereof are omittedhere.

What should be noted about the DC regulated power supply 31 is that areference voltage source 32 generates two reference voltages Vref1,Vref2, and supplies these voltages respectively to differentialamplifiers A1, A2. In the example of FIG. 2, the voltages produced bydividing the input voltage Vin through resistors R01, R02, and R03 areVref1 and Vref2, which are related to each other by Vref1>Vref2.

Further, in the reference voltage source 32, a control transistor Tr0 isprovided parallel to the resistors R02, R03. The control transistor Tr0is ON/OFF controlled by the output of the overheat protection circuit23. When overheated, the control transistor Tr0 is turned on. Thisbrings the reference voltages Vref1, Vref2 to GND level, causing thedifferential amplifiers A1, A2 to cut off the power transistors Q1, Q2and thereby carrying out overheat protection operation.

With the overheated state solved, the control transistor Tr0 is turnedoff to revert from the protected state. In response, the referencevoltage Vref1, which has a closer value to the input voltage Vin risesfirst before the reference voltage Vref2.

Thus, provided that the differential amplifiers A1, A2 have the samegain, by setting different values for the reference voltages Vref1,Vref2 of the respective output systems, i.e., by having differentfeedback voltages Vadj1, Vadj2, it is possible to cause the outputvoltages Vo1, Vo2 of the respective systems to rise at different timingsin reverting from the protected state.

Note that, using capacitors for the resistors R02 and/or R03, it ispossible to extend the delay time of rise in reverting from the overheatprotected state, making it possible to vary the reverting timingaccording to the type of load. The delay time can be set with an RCconstant of the resistor and capacitor.

Third Embodiment

The following describes an electrical structure of a DC regulated powersupply 41 of the Third Embodiment of the present invention. The DCregulated power supply 41 is similar to the foregoing DC regulated powersupply 21, and accordingly corresponding elements are given the samereference numerals and explanations thereof are omitted here.

What should be noted about the DC regulated power supply 41 is thatswitches SW1, SW2 are respectively provided for the lines of referencevoltage Vref supplied to the differential amplifiers A1, A2 from thereference voltage source 22, and that the switches SW1, SW2 arecontrolled by the overheat protection circuit 43. Further, in additionto controlling the switches SW1, SW2, the overheat protection circuit 43in the DC regulated power supply 43 is provided with a delay circuit, soas to vary ON timings of the switches SW1, SW2 when reverting to anormal state from an overheated state.

Thus, detecting an overheated state, the overheat protection circuit 43opens the switches SW1, SW2, so as to suspend the regulation operationsof the control ICs CTL1, CTL2. This prevents interference of regulationoperations between different systems and eliminates regulationmalfunctions due to overheat protection operation, and therebysuppresses fluctuations of output voltages Vo1, Vo2.

Further, in the DC regulated power supply 41, when reverting to a normalstate from an overheated state, the DC regulated power supply 41 is ableto vary, by the operation of the delay circuit, the timings ofreactivating the control ICs CTL1, CTL2 according to the type of load.

Fourth Embodiment

The following describes an electrical structure of a DC regulated powersupply 51 of the Fourth Embodiment of the present invention. The DCregulated power supply 51 is similar to the foregoing DC regulated powersupply 41, and accordingly corresponding elements are given the samereference numerals and explanations thereof are omitted here.

What should be noted about the DC regulated power supply 51 is thatinput voltage Vin of the power supply is supplied to the power lines L1,L2 via a switch SW, and that the switch SW is controlled by an overheatprotection circuit 53. Accordingly, reference voltage sources C1, C2 areinstalled in control ICs CTL1 a, CTL2 a, respectively.

Thus, when an overheated state is detected, power is cut off to suspendthe regulation operations of the control ICs CTL1 a, CTL2 a. Thisprevents interference of regulation operations between the differentsystems and eliminates regulation malfunctions due to overheatprotection operation, and thereby suppresses fluctuations of outputvoltages Vo1, Vo2.

Fifth Embodiment

The following describes an electrical structure of a DC regulated powersupply 61 of the Fifth Embodiment of the present invention. The DCregulated power supply 61 is similar to the foregoing DC regulated powersupplies 41, 51, and accordingly corresponding elements are given thesame reference numerals and explanations thereof are omitted here.

What should be noted about the DC regulated power supply 61 is thatswitches SW1, SW2 are respectively provided for the power lines L1, L2,and that the switches SW1, SW2 are controlled by an overheat protectioncircuit 43. In addition, the overheat protection circuit 43 includes adelay circuit, so as to vary ON timings of the switches SW1, SW2 whenreverting to normal state from overheated state.

Thus, detecting an overheated state, the overheat protection circuit 43opens the switches SW1, SW2, so as to suspend the regulation operationsof the control ICs CTL1 a, CTL2 a. This prevents interference ofregulation operations between the different systems and eliminatesregulation malfunctions due to overheat protection operation, andthereby suppresses fluctuations of output voltages Vo1, Vo2.

Further, in the DC regulated power supply 61, when reverting to a normalstate from an overheated state, the DC regulated power supply 43 is ableto vary, by the operation of the delay circuit, the timings ofreactivating the control ICs CTL1 a, CTL2 a according to the type ofload. Note that, in reactivating the control ICs, the control IC of onesystem may be activated upon detecting activation of the control IC ofthe other system.

The foregoing embodiments described the case where the power transistoris a bipolar-type power transistor. However, the type of powertransistor is not just limited to this example and other powertransistors such as a field-effect power transistor may be used as well.

In order to achieve the foregoing object, a DC regulated power supply ofthe present invention includes: a power transistor provided for eachoutput of a plurality of systems; a control circuit, which compares afeedback value of an output voltage and a reference voltage from areference voltage source, and controls a base current of the powertransistor according to a difference of the feedback value and thereference voltage, so as to regulate the output voltage; and an overheatprotection circuit, which lowers the reference voltage of the referencevoltage source upon detecting an overheated state in the powertransistor.

With this configuration, a DC regulated power supply of a dropper typecan be realized that includes: outputs of multiple systems; a powertransistor serially interposed for each output on a power line thatconnects a DC power supply with a DC load; and a control circuit, whichcompares a feedback value that is obtained from the output voltage witha reference voltage from a reference voltage source, and controls a basecurrent of the power transistor according to the difference and therebycontrols the ON resistance, so as to regulate the output voltage. In thedropper-type DC regulated power supply, in carrying out the overheatprotection operation, the overheat protection circuit of the presentinvention suppresses the output current by lowering the referencevoltage. This contrasts to conventional overheat protection circuits,which suppress the base current of the power transistor to suppress theoutput current.

It is therefore possible to simultaneously suppress the base currents ofdifferent systems and eliminate regulation malfunctions in the overheatprotection operation, thereby suppressing fluctuations of outputvoltage. The present invention is particularly suitable in applicationswhere a control circuit with multiple systems are integrated into onechip and packaged into a single package with the power transistor.

In the DC regulated power supply, the reference voltage source mayprovide a reference voltage for each output of the plurality of systems.

With the foregoing configuration, provided that the differentialamplifier that compares the feedback value of the output voltage withthe reference voltage in the control circuit of one output system hasthe same gain as the differential amplifiers of the other systems, bysetting different values for the reference voltages of the respectiveoutput systems, i.e., by having different feedback voltages, it ispossible to cause the output voltages of the respective systems to riseat different timings in reverting from the protected state.

In the DC regulated power supply, the overheat protection circuit mayinclude: a switch provided for a line of a reference voltage of eachoutput of the plurality of systems; and a delay circuit, provided for atleast one of the switches, that operates when reverting from theoverheated state.

With this configuration, the lines of reference voltages for therespective output systems are separated from one another, and whenreverting from an overheated state, the delay circuit delays the ONtiming of at least one of the switches. This enables each output systemto vary the timing of reactivation according to the type of load.

In order to achieve the foregoing object, another DC regulated powersupply of the present invention includes: a power transistor providedfor each output of a plurality of systems; a control circuit, whichcompares a feedback value of an output voltage and a reference voltagefrom a reference voltage source, and controls a base current of thepower transistor according to a difference of the feedback value and thereference voltage, so as to regulate the output voltage; and an overheatprotection circuit, which cuts off a supply line of an input voltage tothe power transistor upon detecting an overheated state in the powertransistor.

With this configuration, a DC regulated power supply of a dropper typecan be realized that includes: outputs of multiple systems; a powertransistor serially interposed for each output on a power line thatconnects a DC power supply with a DC load; and a control circuit, whichcompares a feedback value that is obtained from the output voltage witha predetermined reference voltage, and controls a base current of thepower transistor according to the difference and thereby controls the ONresistance, so as to regulate the output voltage. In the dropper-type DCregulated power supply, in carrying out the overheat protectionoperation, the overheat protection circuit of the present inventionsuppresses the output current by cutting off the supply line of an inputvoltage. This contrasts to conventional overheat protection circuits,which suppress the base current of the power transistor to suppress theoutput current.

It is therefore possible to suspend the regulation operation of theentire DC regulated power supply, so as to prevent the regulationoperation of one system from influencing the regulation operations ofthe other systems. This eliminates regulation malfunctions in theoverheat protection operation, and thereby suppresses fluctuations ofoutput voltage.

In the DC regulated power supply of the present invention, the overheatprotection circuit may include: a switch provided for a supply line ofeach output of the plurality of systems; and a delay circuit, providedfor at least one of the switches, that operates when reverting from theoverheated state.

With this configuration, the lines of reference voltages for therespective output systems are separated from one another, and whenreverting from an overheated state, the delay circuit delays the ONtiming of at least one of the switches. This enables each output systemto vary the timing of reactivation according to the type of load.

The invention being thus described, it will be obvious that the same waymay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A DC regulated power supply comprising: a power transistor providedfor each output of a plurality of systems; a control circuit, whichcompares a feedback value of an output voltage and a reference voltagefrom a reference voltage source, and controls a base current of thepower transistor according to a difference of the feedback value and thereference voltage, so as to regulate the output voltage; and an overheatprotection circuit, which lowers the reference voltage of the referencevoltage source upon detecting an overheated state in the powertransistor.
 2. The DC regulated power supply as set forth in claim 1,wherein the reference voltage source provides a reference voltage foreach output of the plurality of systems.
 3. The DC regulated powersupply as set forth in claim 1, wherein the overheat protection circuitincludes a switch that is provided for a line of a reference voltage ofeach output of the plurality of systems.
 4. The DC regulated powersupply as set forth in claim 1, wherein: the overheat protection circuitincludes: a switch provided for a line of a reference voltage of eachoutput of the plurality of systems; and a delay circuit, provided for atleast one of the switches, that operates when reverting from theoverheated state.
 5. The DC regulated power supply as set forth in claim4, wherein the delay circuit varies a timing of reverting from theoverheated state with respect to each output of the plurality ofsystems.
 6. The DC regulated power supply as set forth in claim 1,further comprising: a temperature detecting element provided for eachpower transistor.